Many medicaments require infusion into a patient or animal over an extended period of time, rather than in a single immediate dose. Infusion systems are known in the art to allow such medicaments to be so infused in a controlled fashion over a period of time. Such infusion systems generally include an intravenous access point where a medical professional has already placed an “IV” into the patient with medical tubing coupled to a needle penetrating the skin and typically into a vein of the patient. Additionally, such infusion systems include some form of reservoir for containing the medicament to be delivered and some form of infusion device for causing the medicament to move along the infusion tubing and through the IV into the patient.
In perhaps a simplest infusion system, gravity provides the force required by merely placing the reservoir at a height elevated relative to the IV intravenous access point. Gravity fed infusion systems have limitations in that the amount of force cannot be readily changed, other than through the imprecise method of increasing the elevation of the supply reservoir.
In other infusion systems an infusion pump is provided which applies a force on the fluid in the reservoir or along the infusion tubing to cause the fluid to move into the patient at the intravenous access site. One form of infusion pump acts on a medicament containing vessel in the form of a syringe by merely pushing on the plunger of the syringe at its proximal terminal end to deliver a medical preparation from the syringe. Such infusion pumps generally include some form of complicated electromechanical linear displacement transducer which converts an electric signal from a controller into mechanical motion in the form of linear motion acting on the plunger, to cause dispensing of the medical preparation from the syringe reservoir. The linear displacement transducer can be in the form of a solenoid type device or in the form of some form of motor, such as a stepper motor acting upon a rack and pinion type gear to convert rotating motion into linear motion. Other linear displacement transducers can also be utilized within such infusion pumps to convert the electric control signal into mechanical motion.
These electronic infusion pumps have the benefit of being able to utilize electrically driven displays and commonly available buttons and dials for thorough control of infusion rates and volumes, but also have significant deficiencies including a reliance on their internal mechanisms and a continuous source of electricity. If the power supplied from the AC plug or the DC battery is discontinued, full or partial failure of the pump may occur, causing incomplete or inaccurate medication delivery. The pump may also fail with respect to its electronic or mechanical parts within. These sorts of failures often lead to medication errors causing significant patient morbidity and mortality. These complex, expensive pumps increase the cost of delivering medical care, are cumbersome to use, require troubleshooting and frequent service. In addition, some magnetic or electric medical equipment can be interfered with by other equipment containing metal or generating electric signals, presenting a need for non-electric and/or nonmetallic infusion devices. These electronic devices cannot be used near an MRI scanner, but the patients often require ongoing infusion of their medicines, therefore a nonmagnetic/non-electronic device would be desirable.
Accordingly, a need exists for a simple but reliable medicament infusion system which utilizes an infusion device that does not require an electric power supply, can function reliably, and has low cost.
The prior art patents to Yamada (U.S. Pat. No. 5,807,337) and Mitchell (U.S. Pat. No. 5,024,664) demonstrate vacuum powered infusion devices with several limitations and have never attained significant clinical use. These devices connect the drive section to the syringe/load chamber section, which does not allow for independent operation of the two sections. This deficiency does not allow one to use the syringe section to self load by aspiration, nor does it allow one to readily discontinue and/or restart infusion by disengaging or reengaging the drive section from the medicament containing (syringe-like) section. These devices require the user to obtain and load a separate syringe so they can forcefully inject the desired medicament into the load chamber against the vacuum force of the connected drive section through a loading port which is occasionally separate from the infusion port. This obviously requires one to measure and load a separate syringe containing the medicament, attach it to the load chamber of the infusion device and apply an undue amount of finger pressure to force the medicament from the separate syringe into the load chamber as the user must overcome the vacuum force during this filling procedure. These additional steps, such as loading one syringe first to inject medicament into another, greatly increases the chance of medication error. Another limitation with these infusers is the lack of a guide or stabilizer to assure linear translation of the plungers during infusion. If the Yamada or Mitchell device plungers were significantly extended as with a significantly “full” device, there would be degree of rotation, flex and increased “play” in the apparatus which would allow increased friction and unreliable or nonlinear infusion rates. Another limitation of the Yamada and Mitchell devices is the difficulty faced with a loss of vacuum. The Mitchell device does not have a port to reestablish a vacuum should it be lost and the Yamada device has a “plug formed of a resilient material such as rubber” which requires removal in the event the vacuum needs to be replenished or if one wishes to alter the degree of vacuum force. Manipulation of a rubber plug is cumbersome and time consuming. Another limitation of these devices is the lack of a handle to independently operate the drive section. This deficiency is severely limiting and clearly demonstrates these devices are meant to be loaded with medicament only through the use of the second syringe as mentioned above, thereby extending the load chamber and drive section together and not allowing for independent operation of either section. This deficiency yields an inability to rapidly discontinue, start, or restart medicament infusion and maintains the load chamber in an always pressurized state making any attempt at placing medicament into the device cumbersome.
A prior art patent to Minezaki (U.S. Pat. No. 7,041,081) demonstrates a vacuum powered infusion device with many limitations. The device rigidly connects the drive section to the syringe/load chamber section, which does not allow for independent operation of the two sections. These deficiencies do not allow one to use the syringe section to self load by aspiration, nor does it allow one to readily discontinue and/or restart infusion by disengaging or reengaging the drive section from the medicament containing section. The device requires the vacuum section to be cocked back and locked with a “stopper capable of locking the piston at the rear end of the vacuum pump barrel against atmospheric pressure,” before the two sections are placed together, and requires the vacuum barrel to be placed “in a state in which the front end of the vacuum pump barrel of said first structure extends further forward than the front end of the liquid syringe.” One preferred embodiment of this device includes a version with the need for two medicament reservoirs connected together which is complicated and expensive. A second preferred embodiment demonstrates a rigidly aligned coaxial version which does not offer the independent functions required as the two sections are again rigidly connected. Other prior art patents Minezaki (U.S. Pat. No. 6,685,673) and Hiejima (U.S. Pat. No. 6,139,530) also demonstrate coaxial mechanisms with similar limitations.
Accordingly, a need still remains for a simple but effective non-electric self powered infusion device and system for delivering medicament into a patient in a reliable controlled fashion.